A battery pack consists of battery cells connected in series, in parallel or, a combination of both. The battery cells generate heat during discharging and charging. The speed of discharging is positively correlated with the heat generated. A cooling system for the battery pack is very important because a higher temperature or a lower temperature may negatively impact the battery performance as well as battery health conditions. Since multiple cells are connected together, a significant difference in internal temperature values can lead to different charging and discharging rates for different cells and thus cause the battery pack performance to deteriorate. Therefore, the battery thermal management system plays a vital role in the design and operation of the battery pack, and has a direct impact on the performance of the battery pack. In addition, a bad design of a thermal system may result in the BBU failed to function, such as failure to satisfy the backup time needed.
Several conventional battery thermal management systems for cooling electric vehicles exist. These include, for example, the air cooling system, the passive or active liquid system, and the thermo-electric system. However, such systems are insufficient.